The present invention relates to an injection system for intermittent supply of fuel mixtures into combustion spaces of an internal-combustion engine, and to a process for operating such an injection system.
Conventional fuel injection systems generate the required high pressure for the fuel supply into the combustion spaces of internal-combustion engines, such as diesel engines, by way of pumps which are driven directly by the internal-combustion engines. At a low rotational engine speed, the pumping capacity may become insufficient and the fuel distribution may become inaccurate. This leads to power losses and increased pollutant emissions of the internal-combustion engine. These conventional fuel injection systems are also not very variable. In addition, these conventional fuel injection systems are susceptible to inoperability because they have a large number of moving parts.
So-called common rail systems with a central pump for the delivery of the fuel in high-pressure pressure reservoirs and, from there, continuously and without jerking via pipes, to the injection valves uncouple the injection from pressure fluctuations which occur at large. rotational speed differences in the case of conventional pumps driven directly by the engines.
One known common rail injection system ("The Electronically Controlled Dynamic Rail Injection System (DIS)", Ganser-Hydromag) delivers fuel from a fuel reservoir by way of a high-pressure pump into a large-volume pipe system which is connected with injection valves. The injection valves can be actuated by hydraulic pressure, and electromagnetic valves control the opening and closing of the injection valves as a function of operating parameters of the internal-combustion engine. A disadvantage is the high pressure in the injection system, and the high pressure generated by the pump is applied along the entire length of the pipes to the injection openings of the injection valves, even when no injection takes place and a leakage of the fuel can therefore occur, for example, on the connection pieces of the pipes as well as past the closed injection openings into the combustion spaces. Because of safety aspects which must be taken into account during the design phase, the high pressure therefore requires an increased weight and causes problems during the control of the injection system.
DE 24 41 841 A1 shows an injection system for an internal-combustion engine in which a fuel pump and an injection nozzle are integrated in a common housing and in which, by way of the axial displacement of a valve needle. via a control piston and a pressure generator, the fuel is injected from a distributing space into the combustion space of the internal-combustion engine. A readjusting pressure spring is provided for the valve needle. In this known injection system, the function of the control of the valve needle cannot be separated from the pumping operation, and variability is very limited with respect to the control and the pressure level. This known injection system does not solve the existing problem of the high-expenditure design because of high storage pressures in common rail injection systems.
DE 40 27 493 A1 describes an injection nozzle for an internal-combustion engine in which the valve needle is loaded at intervals by two different locking springs in order to achieve a control of the injection pressure over time.
It is an object of the present invention to provide an injection system for the intermittent feeding of fuel mixtures into combustion spaces of an internal-combustion engine and a process for operating this injection system for the intermittent feeding of fuel mixtures which permits a simple control and the providing of standardized parts, for example pumps, which results in low weight and avoids leakage.
This object has been achieved in accordance with the present invention by an injection system for the intermittent feeding of fuel mixtures into combustion spaces of an internal-combustion engine, comprising an injection nozzle and an injection pump integrated in a common housing. An injection valve has a valve member configured to be movable along a longitudinal axis of the injection valve to selectively expose and close an injection opening. A rearward end of the valve member is connectable with a piston configured and arranged to be axially movable in a cylinder bore of the housing. A side of the piston facing the opening, together with the cylinder bore, forms a control space configured to be acted upon by a control pressure. A sleeve-shaped control piston is arranged coaxially to the valve member. One end of the control piston projects into the control space and another end of the control piston projects into a fuel distribution space above the opening. A side of the piston facing away from the opening and the side of the control piston facing the opening each are acted upon by a pressure spring, and a control valve permits the fuel supply from a pressure source of an increased pressure to the fuel distribution space.
Moreover, a method according to the present invention is characterized by connecting the control space with the pressure source for providing the increased pressure so that the valve member exposes the injection opening, moving the piston toward the injection opening, injecting fuel mixture, thereafter connecting the control space with a lower pressure so that the valve member closes the injection opening, and moving the piston away from the injection opening while the pressure is reduced and no injection takes place.
According to the present invention, an injection system for the intermittent feeding of fuel mixtures into combustion spaces of an internal-combustion engine comprises hydraulically actuated injection valves which each contain a valve member and a piston. Fuel mixture is continuously fed to the injection valves at a predetermined pressure. A valve member and a piston form a variable control space which, by way of a switchable valve, which is connected alternatively with a device for providing an increased pressure (p1) or with a pipe with a much lower pressure (p0). A first pressure spring acts upon the valve member and a second pressure spring acts upon the piston, the first pressure spring having a larger spring rate than the second pressure spring.
The amount of the fuel mixture supplied into the combustion space per injection is determined by the switching positions of the valve for the control space. When the control space is connected with the pipe with the pressure (p0), the valve member is pressed by the first pressure spring onto an injection opening of the injection. valve so that no injection will take place. At the same time, the second pressure spring presses the piston away from the injection opening so that the space in front of the injection opening is enlarged, and the pressure in the space in front of the injection opening of the injection valve is rapidly reduced (rapid end of injection; no afterinjection). When the control space is connected with the pipe with the pressure (p1), the valve member is lifted off the injection opening of the injection valve so that the injection will take place. At the same time, pressure (p1) presses the piston toward the injection opening so that the space in front of the injection opening is reduced, and the pressure at which the fuel mixture is transported through the injection opening of the injection valve is rapidly increased.
The injection system according to the present invention can be operated by a clearly lower pressure than a conventional common rail injection system and results in less afterinjection into the combustion space of the internal-combustion engine and in lower leakages at the connection points. Accordingly, the injection system can be equipped with standardized parts, particularly with a standardized pump for generating pressure, and can therefore be manufactured at low cost and have a lower weight than an injection system which must be sized for higher pressures.
By the use according to the present invention of hydraulic oil or engine oil, a medium for the control of the injection system is provided which is particularly suitable for the transmission of p0 and p1 pressures.
The pressure (p1) for the control of the injection system according to the present invention may be generated by a mechanically operated pump, such as a cam plunger pump. A magnetic valve on the pump can limit the pressure (p1) in the injection system. The pressure (p1) for the control of the injection valve can be provided by a central pressure accumulator so that, independently of the rotational speed of the internal-combustion engine, a constant pressure is available for controlling the injection valve.
According to an advantageous aspect of the injection system according to the present invention, fuel mixed with a second suitable liquid, such as water, is delivered in a common pipe in front of the injection opening.
By way of a throttle in a pipe from the valve to the control space and a bypass pipe in parallel to the pipe from the valve to the control space, the pressure in the control space can be modulated. The injection can, therefore, be controlled in a targeted manner so that the fuel consumption and the pollutant emissions of the internal-combustion engine as a whole can be reduced.
According to the present invention, the injection system of the invention can be particularly easily controlled by actuating a valve and, in addition, as required, by actuating a throttle.